Friction vacuum pump

ABSTRACT

A friction vacuum pump ( 1 ) comprises a fixed element ( 7 ) bearing rows of stator blades ( 3 ) and a rotating element ( 6 ) bearing rows of rotor blades ( 2 ). The rows of stator blades and rotor blades are arranged concentrically with respect to an axis of rotation ( 4 ) of the rotating element ( 6 ) and mesh with each other. In order to create in the axial direct a short friction pump, the elements ( 6, 7 ) bearing the rows of rotor blades and stator blades extend in a substantially radial manner and the longitudinal axes of the blades ( 2, 3 ) extend in a substantially axial manner.

BACKGROUND OF THE INVENTION

The present invention relates to a friction vacuum pump comprising afixed element bearing rows of stator blades and a rotating elementbearing rows of rotor blades whereby the rows of stator blades and rotorblades are arranged concentrically with respect to the axis of rotationof the rotating element and engage with each other.

Turbomolecular vacuum pumps are a kind of friction pump, see for exampleU.S. Pat. No. 5,577,883. They are designed just like a turbine with rowsof rotor and stator blades. Stator and rotor are substantiallycylindrical in shape and are arranged coaxially with respect to therotational axis of the rotating component. The longitudinal axes of thestator and rotor blades which engage in alternating fashion, extendradially so that a substantially axial direction for the pumping actionresults. One or several pairs of a row of rotor blades and a row ofstator blades form a pump stage. The pumping properties (pumpingcapacity, compression) of a pump stage are adjusted through the designof the blades, preferably through their angle of incidence.

In the instance of turbomolecular vacuum pumps according to thestate-of-the-art, there exists a minimum requirement for the number ofpump stages, which can not be reduced any further. Thus turbomolecularvacuum pumps according to the state-of-the-art have to be relativelylong, in particular since the drive motor contributes further to theaxial length. Moreover, in the instance of the known turbomolecularvacuum pumps only one component—commonly the rotor—can be made of asingle piece, whereas the other component—commonly the stator—needsconsist of a multitude of components in order to be able to assemble theengaging rows of stator blades.

It is the task of the present invention to create a turbomolecularvacuum pump of the aforementioned kind which is significantly shorter inthe axial direction.

This task is solved by the present invention through characterisingfeatures of the patent claims.

SUMMARY OF THE INVENTION

The present invention allows the manufacture of friction pumps, theaxial length of which—disregarding the drive motor—does notsignificantly extend beyond the length of the stator and rotor blades.Since the blades extend axially, both rotor and stator may be made of asingle part respectively.

It is expedient to operate radially pumping pumps of the kind accordingto the present invention, in such a manner that the pumped gases flowfrom outside to inside. Here the utilisation of the differingcircumferential speeds of the blades offers an advantage, sincecorresponding to the pressure range the frictional losses can bereduced. Moreover, the losses owing to backflowing gas can be muchreduced in the direction of the pumping action compared to the axialcompressor, since the stator may be manufactured as a single part andsince no tolerances will add owing to a multitude of components needingto be joined. Equally the losses due to backflowing gas flowing aroundthe tips of the blades are minimised, since here too the slots can bereduced significantly by aligning the carriers.

A further advantage exists in that the detailed rotor disks can bemanufactured on lathes or erosion machines. Both techniques arerelatively cost-effective. With the attainable reduction in the numberof parts, the present invention represents a true alternative in meetingtoday's pressure on prices.

Moreover, it is expedient to combine known axially compressingturbomolecular vacuum pumps with radially compressing friction vacuumpumps designed according to the present invention. Pump systems of thiskind allow the placement of the drive motor on the high vacuum sidewithout the need for the motor and the bearings to consist ofhigh-vacuum capable materials. Finally, there result advantages relatingto the bearing arrangement for the rotating component. Long rotorsrequire, in particular when they are to be suspended in a cantileveredmanner, relatively involved bearings which in the instance of therelatively short rotors in the friction vacuum pumps according to thepresent invention are no longer necessary.

Still further advantages of the present invention will become apparentto those of ordinary skill in the art upon reading and understanding thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating a preferred embodiment and are notto be construed as limiting the invention.

FIG. 1 depicts a radial section through the blades of a friction vacuumpump according to the present invention,

FIGS. 2 to 4 depict axial sections through different embodiments,

FIGS. 5 and 6 depict sections through a double-flow embodiment,

FIG. 7 depicts a section through a multi-stage solution,

FIG. 8 depicts a combination of a radially pumping pump stage withaxially pumping friction pumping stages as well as, and

FIGS. 9 to 11 depict combined friction vacuum pumps for multi-chambersystems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts an embodiment of a friction pump 1 according to thepresent invention, in which the longitudinal axes of blades 2, 3 extendparallel to a rotational axis 4 of the rotating component. They arearranged in concentric rows about the rotational axis 4. The rows ofrotor blades 2 and the rows of stator blades 3 alternate. They engageinto each other and have changing angles of incidence in the directionof flow (arrow 16) in a basically known manner.

FIGS. 2 to 4 depict an embodiment in which the blades 2, 3 arecomponents of rotating and fixed carriers respectively, 6 and 7. In thedesign example according to FIG. 2 the rotating carrier 6 and the fixedcarrier 7 have the shape of a disk. In the embodiment in accordance withFIG. 3, the surface on the blade side of the stator disk 7 is designedto be cone-shaped in such a manner that the distance between the twodisks 6, 7 decreases from outside to inside. Also the length of theblades 2, 3 decreases from outside to inside.

In the embodiment in accordance with FIG. 4, the fixed carrier 7 has theshape of a funnel so that the distance between the carriers 6 and 7decreases from inside to outside. The length of the blades 2, 3 isadapted to this change in distance.

In the embodiment of FIG. 4, the fixed carrier 7 is part of a casing 8of pump 1. It includes the carrier 7 with connecting port 9 as well asof a flat, pot-shaped casing section 11 which at its rim is flanged tocarrier 7. A bottom 12 of the casing section 11 extends parallel torotor disk 6. Said bottom carries the drive motor 13, the shaft 14 whichengages the rotor disk 6 through an opening in the bottom 12. Moreover,there is provided at the casing section 12 a further connecting port 15.

Vacuum pumps are preferably operated such that the pumping chamberdecreases in the direction in which the gases are pumped. Frictionvacuum pumps 1 according to the present invention offer this propertyalready when the gases are being pumped from outside to inside (c.f. thearrows 16 drawn in to FIGS. 1 to 3). The design of the fixed carrier 7in accordance with drawing FIG. 3 even strengthens this property. Alsothe width of the blades 2, 3 may decrease from outside to inside (c.f.FIG. 1 in particular).

Of course, operation of the friction pumps is possible in the reversepumping direction. To this end only the direction of rotation for rotor6 needs to be reversed. An example of a friction pump 1 being operatedin this manner is depicted in FIG. 4 (arrows 18). The connecting flange9 forms the inlet, the connecting flange 15 the outlet of the pump. Tochange the direction of the pumped gases, the pump chamber is modifiedsuch that the distance of the carriers 6, 7 and thus the lengths of theblades 2, 3 decrease from inside to outside.

Depicted in FIGS. 5 and 6 is a double-flow embodiment of a frictionvacuum pump 1 according to the present invention. An inner group of rowsof blades pumps the gases radially towards the outside (arrows 21), anouter group of rows of blades from outside to inside (arrows 22). Theconnection ports 9 and 15 are inlet ports. Between the two groups, thestator disk 7 is equipped with a connection port 23 having the functionof an outlet. By reversing the direction of rotation there results afurther configuration (one intake port, two discharge ports), as may beutilised for leak detectors, the operation of which is based on thecounter flow principle. Finally there also exists the option ofdesigning the friction pump 1 according to the present invention asmultiple-flow pump, i.e. with several groups of blades, which—comparedto their neighboring groups of blades in each instance—have an opposingdirection for the pumping action.

In the design example according to FIG. 7, several radially pumping pumpstages are located axially in the casing 8 over each other. The rotatingsystem comprises two rotor disks 6, which each carry on both sides rotorblades 2. The casing 8 and a carrier 25 affixed to the casing, saidcarrier being located between the two rotor disks 6, carry thecorresponding stator blades 3.

Drawn in arrows 27 indicate that the connection port 9 has the functionof an inlet and that the subsequent radially compressing stages (four,in all) pump from inside to outside and from outside to inside inalternating fashion. The outlet is designated as 26. It is locatedinside and surrounds the drive shaft 14 so that in this area no sealingagents are required. By adapting the length of the blades from the inletto the outlet (decrease) it is again possible to influence the volume ofthe pump chamber.

FIG. 8 depicts an option in which radially compressing friction vacuumpump 1 according to the present invention may be combined with anaxially compressing friction pump 31 according to the state-of-the-art.The friction pump 31 consists of a turbomolecular pumping stage 32located on the intake side and a molecular pumping stage 33 located onthe delivery side, said molecular pump being designed as a Holweck pump(as depicted) or as a Gaede, Siegbahn, Engländer or side channel pump.

The friction pumps 1 and 31 are located in a joint, approximatelycylindrically-shaped casing 35 with an inlet 36 at the side. A shaft 39supported by bearings at both face sides (bearings 37, 38) carries therespective rotating components of the pumping stages (rotor disk 6 ofthe radially compressing pump 1, rotor 41 of the turbomolecular pumpingstage 32, cylinder 42 of the Holweck pumping stage 33). The side inlet36 of the combined pump opens out between the radially compressingpumping stage 1 and the axially compressing pump 31. The outlet 44 ofthe combined pump is located on the delivery side of the molecularpumping stage 33. The drawn in arrows 45 and 46 indicate that theradially compressing pump stage 1 takes in the gases which are to bepumped in the area of its periphery, and that the axially compressingpump 31—as is common—takes in the gases in the area of its high-vacuumside. The gases being pumped by pump stage 1 pass via a bypass 47directly to the intake side of the Holweck pumping stage 33.

The special characteristic of the solution in accordance with drawingFIG. 8 is, that the drive motor 48 is located at the high-vacuum side ofthe axially pumping pump 31 (and not as is common on the delivery sideof the Holweck pumping stage 33). In that the radially compressingpumping stage 1 is located between the inlet 36 and the drive motor 48,a relatively high pressure (1×10⁻² mbar, for example) can be maintainedin the motor chamber 49. The use of high-vacuum capable materials inmotor chamber 49 is not required. Moreover, the radially pumping pumpstage 1 supports the pumping capacity of the turbomolecular pumpingstage 32 without significantly increasing the length of the pump 31.

FIGS. 9 to 11 depict embodiments of combined friction pumps fordeployment in connection with multi-chamber systems, a two-chambersystem in this instance. These are, for example, analytical instrumentswith several chambers which need to be evacuated down to differentpressures. Thus the distance of the intake ports is given, which in theinstance of the state-of-the art frequently results in the requirementfor relatively long cantilevered rotor systems which in turn requireinvolved bearing systems.

All embodiments in accordance with FIGS. 9 to 11 have two side inlets36, 36′. These are separated by at least one radially compressingpumping stage 1. The inlet 36 “sees” in each instance, as also in theembodiment according to drawing FIG. 8, the inlet areas of an axiallypumping friction pump 31 as well as a friction pump 1 pumping radiallyfrom outside to inside.

In the embodiment in accordance with FIG. 9, the outlet of the radiallypumping pump 1 opens out into the inlet area of a second turbomolecularpumping stage 32′ to which the second inlet 36′ is connected. The pump 1has the effect that the pressure at inlet 36 is lower than at inlet 36′.The drive motor 48 is located on the delivery side of the turbomolecularpumping stage 32′. Said delivery side is linked via a bypass 47 to thesuction side of the molecular pumping stage 33.

If pumping of a partial flow from the inlet 36 into the area of theinlet 36′ is not desired, a further axially compressing friction vacuumpump 1′ may be provided for separating the inlets 36, 36′ (FIG. 10). Itpumps a partial flow of the gases entering into the inlet 36′. Theoutlets of the two friction pumps 1 and 1′ are linked to the bypass 47.

The embodiment in accordance with FIG. 11 has instead of theturbomolecular pumping stage 32′, a further axially pumping frictionpump 1″. This solution may be employed when the amount of gas is notgreat.

In the embodiments in accordance with FIGS. 9 to 11, there are providedin each instance two high-vacuum pump systems 32, 32′, 1″ each connectedwith an inlet 36 and 36′. The selected arrangement also permits thearrangement of further high-vacuum pumps on the common shaft 39 and toseparate their inlets each by radially pumping pump stages designed inaccordance with the present invention. Through bypasses, both thehigh-vacuum pumping stages, generally turbomolecular pumping stages andalso the outlets of the radially pumping pump stages can be linked eachto a joint molecular pumping stage.

The presented examples demonstrate that the combination and the sequenceof the pumping stages can be selected at will, and can be adapted to thespecific application requirements. The arrangement of the pumping stagesallows for more compact designs with bearings at both shaft ends. Thusthe shafts can be made as stiff as needed. This results in designs whichare unproblematic as to the rotor dynamics, and which also exhibit agood balancing characteristic. In that almost any number of stages canbe attached to the shaft just like the components of a modular system,it is easier to implement a high-vacuum pump which compresses againstthe atmosphere.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

1. A friction vacuum pump comprising: a common cylindrical housinghaving an entrance opening and a discharge opening; a shaft rotatablymounted in the common housing and extending along an axis of rotation; afirst pumping stage mounted to the rotor shaft and having an inletadjacent the housing inlet, the first pumping stage including: aplurality of rows of stationary stator blades mounted on an elementfixed to the housing, a plurality of rows of rotor blades carried by arotating element arranged on the shaft for rotation around the axis ofrotation, a longitudinal axis of the blades extending substantiallyaxially, the rows of stator blades and the row of rotor blades beingarranged concentrically with respect to the axis of rotation and meshingwith each other, the rotor blades and the stator blades being canted toa radial direction such that as the rotating element rotates, a flowthrough the pump is directed radially from an outside inlet disposedadjacent the housing inlet to an inside outlet adjacent the shaft, asecond pumping stage mounted on the shaft in the common housing adjacentthe housing inlet, the second pumping stage including: an outercylindrical stator with inwardly extending rows of stator blades, aninner cylindrical rotor with radially outward extending rows of rotorblades, the rows of stator blades and the rows of rotor blades beingarranged concentrically with respect to the axis of rotation and meshingwith each other, a longitudinal axis of the second stage stator androtor blades extending in a substantially radial direction, the secondstage rotor and stator blades being canted to the axial direction, suchthat as the rotor rotates, a flow through the second pumping stage isdirected axially from an axially located inlet adjacent the casing inletto an axially located outlet in communication with the casing outlet;the first pumping stage being arranged on the shaft at the inlet side ofthe second pumping stage; the common housing entrance opening beinglocated between the first and second pumping stages.
 2. The frictionvacuum pump according to claim 1, wherein a length of the first pumpingstage rotor and stator blades at least partially decrease from outsideto inside.
 3. The friction vacuum pump according to claim 2, wherein awidth of the first pumping stage rotor and stator blades decreases fromoutside to inside.
 4. The friction vacuum pump according to claim 1,further including: a plurality of radial pumping stages arranged axiallywith the first pumping stage, one after the other.
 5. The frictionvacuum pump according to claim 4, wherein at least one of the firstpumping stage rotating and fixed elements has blades on opposite faces.6. The friction vacuum pump according to claim 1, further including: adrive motor located in a motor chamber of the housing for driving therotating shaft.
 7. The friction vacuum pump according to claim 6,wherein the first pumping stage separates a high vacuum side of thesecond pumping stage from the motor chamber.
 8. The friction vacuum pumpaccording to claim 1, wherein the second pumping stage includes at leasta first pumping step and a second pumping step arranged axially, thesecond pumping step having an inlet which is linked to an outlet of thefirst pumping step.
 9. The friction vacuum pump according to claim 8,wherein the first step is a turbomolecular vacuum pump step and thesecond step is a molecular vacuum pump step.
 10. The friction vacuumpump according to claim 9, wherein the outlet of the first pumping stageis connected to the inlet of the second step of the second pumpingstage.
 11. The friction vacuum pump according to claim 1, furtherincluding: a third pumping stage arranged on the shaft oppositely to thesecond pumping stage such that an inlet of the third pumping stage facesthe first pumping stage; the cylindrical housing further including asecond entrance opening between the first and third pumping stages. 12.The friction vacuum pump according to claim 11, wherein the inlet of thefirst pumping stage is connected with the first housing entrance betweenthe first and second pumping stages.
 13. The friction vacuum pumpaccording to claim 11, wherein the second pumping stage includes atleast first and second axially arranged pumping steps, each pumping stephaving an inlet and an outlet, the outlet of the first step beingconnected with the inlet of the second step and the outlet of the thirdpumping stage being connected to the inlet of the second step of thesecond pumping stage.
 14. The friction vacuum pump according to claim13, wherein the third pumping stage is configured the same as the secondpumping stage.
 15. The friction vacuum pump according to claim 13,wherein the third pumping stage is constructed like the first pumpingstage.
 16. The friction vacuum pump according to claim 11, wherein thefirst pumping stage includes first and second radial pumping stepshaving first and second inlets, the first radial pumping step inletsbeing linked with the first housing opening and the second radialpumping step inlet being connected with the second housing entranceopening, the first and second radial pumping steps having a commonoutlet; the second pumping stage includes at least first and secondaxially arranged pumping steps, each having an inlet and an outlet, theoutlet of the first second stage step being connected with the inlet ofthe second second stage step; the common outlet of the first and secondradial pumping stages being connected with the inlet of the second stepof the second pumping stage.